The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Systems using fluid such as water to cut material precisely are well known. Typically, such systems place the fluid under extreme pressure (e.g. 30,000 psi or higher) and force the fluid through an aperture or orifice so as to be discharged at a high velocity upon the material to be cut through an erosion process. In many applications, an abrasive is also introduced into the fluid stream and discharged with the fluid to improve the efficiency of the cutting action by enhancing the erosion process.
Using a fluid stream to cut material produces cuts with characteristics different than those made with conventional cutters. Both FIGS. 1 and 2 illustrate a fluid stream 10 exiting an orifice 12 of a nozzle 14 to cut a workpiece 16. Typically, more than a hole is desired in the workpiece 16 so the nozzle 14 and hence the fluid stream 10 are moved along a desired path 15 relative to the workpiece 16. In FIG. 1, the nozzle 14 moves in and out of the page, while in FIG. 2 the nozzle 14 moves in the direction indicated by arrow 15.
Referring to FIG. 1, the resulting cut 20 made by the fluid stream 10 has a width on a top surface (facing the nozzle 14) that differs in width from the bottom surface 24 (facing away from the nozzle 14). The resulting taper 28 due to the difference in widths is referred to as the “Kerf angle” 30. Stated another way, the Kerf angle 30 is the angle the cut face 32 is out of parallel from the fluid stream axis (the stream is often not normal to the material surface by design). The taper 28 is a function of material thickness, but also is a function of cutting speed or movement of the nozzle 14. In general, the taper 28 becomes less as cutting speed slows, and then as cutting speed further slows beyond a point, the taper 28 reverses from that illustrated in FIG. 1 becoming narrower toward the surface 22. Compensation for the taper 28 typically includes tilting the nozzle 14 relative to the workpiece 16 about the axis of motion of the nozzle 14.
In addition to the taper 28 present in the cut, a “lag” is present due again to the thickness of the material and movement of the nozzle 14. Referring to FIG. 2, the faster the nozzle 14 moves, the more the fluid stream 10 is deflected by the material of the workpiece 16. As illustrated, a deflection distance 32 is defined as the difference in length between the point where the fluid stream 10 impinges the top surface 22 and where the stream 10 exits the bottom surface 24, whereas a “Kerf lag” can be defined as an angle 34 using a straight line 36 formed between these points. Typically, the Kerf lag 34 does not affect cutting accuracy when cutting a straight line since the exiting portion of the fluid stream 10 follows the impact point. However, on corners, for example, the deflection of the fluid stream 10 can cause cutting errors as it flares to the outside of a corner leaving behind or cutting undesirable deflection tapers. Furthermore, the finish of even straight line cuts is affected by the speed of the nozzle 14. However, unlike the taper 28, the lag 34 may be reduced by slowing the motion of the nozzle 14 across the workpiece 16. Like the taper 28, tilting of the nozzle 14, in this case, about an axis transverse to the direction of motion can also provide some compensation for the lag 34.
Systems have been advanced using compensation for Kerf errors, nevertheless improvements are desired.